It was a marriage contract penned for the unity and peace of two kingdoms before either had children. Due to the nature of the contract it was written with vague wording, though neither king expected what would actually come to pass. The mighty King of the larger kingdom and sprawling empire had only one child, a son. The king of the smaller kingdom, a center of art and culture, had two sons one much younger than the other. No daughter was ever born and when the heir of the mighty king, now the king himself, caught sight of the second prince he knew he had to enforce the contract and make the beautiful prince his own.
I would love to play the younger prince sent to the empire as an ambassador as a way of fulfilling the contract but the older prince, now king, wants him just as the contract dictates.